1. Field of the Invention
This invention relates generally to echo cancellation in audio/video systems. More specifically, this invention relates to generating adaptive thresholds for use in an echo canceller in two-way audio/video systems.
2. Description of the Related Art
There are four “talk” states in two-way audio and video systems. The first is “near endpoint only” where there is talk only at the local end. The second talk state is “far endpoint only” where there is talk only at the remote end. The third is double talk where there is talk at both ends at the same time. And the fourth talk state is idle, where both ends are quiet.
Among the four talk states, echo cancellation during the double talk state presents the most challenge. This is because there are no echoes in the near endpoint only and idle states, and it is relatively easy to suppress echo in a far endpoint only state. During the double talk state, however, the amount of noise suppression applied to voice signals must be reduced to avoid filtering out the near endpoint audio signal.
In previous audio and video systems, fixed thresholds are used to detect double talk in voice signals. To determine the thresholds, static measurements are taken during development of the system, to get the energy levels of the voice input signal from the microphones during each of the talk states. During the double talk state, the energy level is typically higher than the level measured during the far endpoint only state. During development, measurements of voice signals are made using a particular physical set-up of rooms, equipment, and speaker geometry. When the systems are deployed, however, different equipment and room arrangements are used, and the use of static thresholds for echo cancellation may result in sub-optimal system performance.
Further difficulties with echo cancellation arise when the system is in a noisy room, when the microphone is positioned closer to the speaker than expected, and when another manufacturer's equipment is substituted for the original equipment in the system. These factors are particularly important with the growing popularity of video and audio conferencing using personal computer systems, hand-free cellular telephones, and speakerphones.
Thus it is desirable to provide video and audio systems that include echo cancellation filters with thresholds that adapt to changes in equipment, position of the equipment, and room geometry.